java - 什么时候可以使用 "=="运算符？

Question

我找到了 jls 的引用:

The equality operators may be used to compare two operands that are convertible (§5.1.8) to numeric type, or two operands of type boolean or Boolean, or two operands that are each of either reference type or the null type. All other cases result in a compile-time error.

但是这段代码

   String str= "";
   Number num = 1;
   System.out.println(str == num);

每个操作数都是引用!

表示这是不兼容的类型。

jls 中哪里说这些类型应该兼容？

Answer 1

在 section 15.21.3 (引用相等运算符 == 和 !=):

It is a compile-time error if it is impossible to convert the type of either operand to the type of the other by a casting conversion (§5.5). The run-time values of the two operands would necessarily be unequal.